The present invention relates to a photographing lens used for a lens-fitted film unit or a fixed focus camera.
Recently, lens-fitted film units have come into wide use because they function as handy inexpensive cameras. There is a demand for more handy cameras, the image quality of which is high. Conventional examples of a lens-fitted film unit composed of a single lens are disclosed in Japanese Patent Publication Open to Public Inspection Nos. 199351/1988 and 106710/1990. Conventional examples of a lens-fitted film unit composed of two lenses are disclosed in Japanese Patent Publication Open to Public Inspection Nos. 307712/1989, 211215/1992 and 281465/1993.
The above conventional examples of a lens-fitted film unit composed of a single lens are disadvantageous in that: it is impossible to correct lateral chromatic aberration so that the color bleeding is remarkable in the periphery of the image plane and further distortion is increased. When a distance from the lens to the film surface is shortened so as to reduce the thickness of the camera, image quality is remarkably affected by the aberration.
According to the structure including two lenses disclosed in Japanese Patent Publication Open to Public Inspection No. 307712/1989, a positive and a negative lens are combined so as to correct lateral chromatic aberration, however, distortion is remarkable. According to the structure including two lenses disclosed in Japanese Patent Publication Open to Public Inspection No. 211215/1992, two positive meniscus lenses of Hypergon are arranged on both sides of a diaphragm substantially symmetrically to each other, so that it is easy to correct lateral chromatic aberration and distortion, however, the telephoto ratio is high. Accordingly, unless the focal length is shortened, the entire lens length is increased, so that the thickness of a lens-fitted film unit is increased.
The entire length of the lens disclosed in Japanese Patent Publication Open to Public Inspection No. 281465/1993 is shorter than that disclosed in Japanese Patent Publication Open to Public Inspection No. 211215/1992. However, the lens disclosed in Japanese Patent Publication Open to Public Inspection No. 281465/1993 has been subjected to correction of lateral chromatic aberration for panoramic printing. Accordingly, a barrel-shaped distortion remains, so that a long side of the image plane is distorted into a barrel shape.